The research aims at a comparison of howler monkey (Alouatta) populations from two major habitat types in Venezuela: 1) montane forest, and 2) gallery forest of the llanos. In the llanos habitat two sites will be compared: a) the first study area has only Alouatta, b) the second study area has both Alouatta and Cebus. Productivity of the two habitat types will be measured in an effort to assess the carrying capacity for the two regions. A time, energy budget for Alouatta will be established together with a detailed analysis of feeding patterns. Population parameters including natality, mortality and net recruitment will be calculated for the two areas. Male replacement in established troops will be given special emphasis in the llanos study site. A complete analysis of the llanos population will provide unique data for a primate species in gallery forest. The population studies in the montane forest will provide comparative data relevant to current and past studies in Panama and Mexico.